Processing of Ceramic Matrix Composites by Pulsed-CVI and Related Techniques

Abstract

P-CVD/CVI is used to densify model pores and to fabricate Nicalon/SiC microcomposites with pyrocarbon or (PyC-SiC)/sub n/ multilayered interphases. The gaseous precursors are hydrocarbons (CH/sub 4/ or C/sub 3/H/sub 8/) for pyrocarbon and CH/sub 3/SiCl/sub 3/-H/sub 2/ for SiC. The best densification conditions for 60; 120 and 320 mum model pores, by pyrocarbon, are T=900-1000degC; P/sub 2/=1-3 kPa and t/sub R/=a few s. Even under such conditions, a thickness gradient is always present along the pore axis. Filling ratios as high as 90% are observed for the largest pores. Smooth or rough laminar pyrocarbon is deposited depending on the value of t/sub R/ and hence the maturation of the gas phase. Multilayered (PyC-SiC)/sub n/ interphases (with n=10-30; e(PyC)=3-50 nm and e (SiC)=10 or 30 nm) act as mechanical fuses and are more resistant to oxidation than pyrocarbon interphase. P-CVD/CVI can be used to elaborate highly engineered new ceramics